Many dipped rubber goods are disposable items, for example, gloves. Some gloves are made from natural rubber called “Latex” gloves, some are made from synthetic rubber, called “Nitrile” gloves.
The rubber material is relatively expensive. In order to reduce cost, it is loaded with less expensive fillers. One such example is calcium carbonate, CaCO3.
Various fillers can have different effects on the properties of rubber. Some fillers when added in access, can deteriorate the physical properties of rubber. Excess amount of fillers disturbs the structure of the rubber. When subject to testing, the rubber will break more easily. Some fillers can be beneficial to physical properties of the rubber. Silicon dioxide (SiO2), in miniature particles, called fumed silica, can enhance physical properties, even if added in small amounts. It is not clear how the miniature particles or nanoparticles of fumed silica enhance properties. One possibility is that they are embedded in between the cured rubber particles and act like a glue. Some filler can change the rubber's appearance. For example, titanium oxide (TiO2), which is added to grant the rubber opacity.
Calcium Carbonate (CaCO3) is used in gloves for a long time. It is the most popular glove filler. Rubber filling is continued to be discussed in the literature.
There are a few varieties of CaCO3, mined and manufactured. The most common is mined CaCO3. It is dispersed in water and added to aqueous latex dispersions as such. Another, a more expensive version, is precipitated CaCO3. It is made as follows:                Mining high purity calcium carbonate rock;        Crushing the rocks to the particle size such as small stones or powder and separating some impurities from the crushed rock;        Calcining (heating) in a kiln to 1,000° C., which takes the calcium carbonate apart, forming lime (CaO) and carbon dioxide gas (CO2), where the carbon dioxide can be captured for reuse;CaCO3+Heat→CaO+CO2↑        Adding the lime to water to form calcium hydroxide (hydrated lime or slake);CaO+H2O→Ca(OH)2         Separating out additional impurities from the slaked lime; and        Combining the captured carbon dioxide with the slaked lime, where calcium carbonate reforms, and since it is insoluble in water, it precipitates out.Ca(OH)2+CO2→CaCO3↓+H2O        
Such CaCO3 has many applications, for example in cosmetics and in tooth paste. It can also be dispersed in water and added to the aqueous rubber latex dispersion.
When comparing mined CaCO3 with precipitated CaCO3 as a rubber filler, the mined CaCO3 is the one used regularly in gloves as such. The precipitated CaCO3 is a more expensive, unique product.
Precipitated CaCO3 have been used in rubber in special applications. For example, in surgical gloves which needs sterilization. When standard CaCO3 filled, surgery gloves were sterilized with gamma irradiation, the gloves became discolored. This problem was solved by using the more expensive, precipitated CaCO3. It could stand the gamma rays sterilization. However, the rubber discoloration problem is solved now by sterilization with ethylene oxide gas in sealed chambers and more recently, by using an electron beam radiation sterilization. There is no need for the more expensive precipitated CaCO3 for this application.
For precipitated CaCO3 and electrical conductivity, there is a difference between the electrical properties of mined CaCO3, and precipitate CaCO3. At the time of preparation, described as above, some water molecules join the CaCO3 precipitate crystal. As a result, precipitated CaCO3 is a hydrated material.
As said, precipitated CaCO3 was used before to protect sterilized rubber gloves from gamma radiation. It is possible that such captured water molecules can stop the free radical irradiation damage at its initial stages and prevent further free radical reactions and damage of discoloration to the rubber. Precipitated CaCO3 when used as a filler, adds water molecules to the cured rubber system. Water is a good conductor of electricity. In relation to the invention, the presence of water-containing fillers, in specific, precipitates calcium carbonate, will help rubber gloves to have a better electrostatic discharge (ESD) properties.
For Azo pigments and their electrical properties, most pigments contain heavy metals. Such pigments might cause rubber to be more conductive. However, heavy metals are not desirable in sensitive electrical manufacturing environments. Organic Azo pigments are heavy metal free. Azo molecules contain conjugated double bonds of nitrogen and of carbon and are known to be electrically active. It is discussed that Azo dyes can increase ESD properties. In relation to the invention, adding Azo dyes as a pigment helps to improve ESD properties of latex gloves.
For electrical conductivity, a non-ionic pigment granting rubber to have a better static discharge is carbon black. This is known in the literature.
Carbon Black filling enhances the ESD effect of rubber. In addition, carbon was shown to increase conductivity by reaction with chlorine fixation on anthracites. This is known in the literature, carbon black and its effect on electrical resistivity. In relation to the invention chlorination of carbon black filled rubber glove is helpful to ESD.
For the conductivity of chlorinated rubber films, chlorination by itself will change the structure and properties of rubber. One example is rubber chlorination. Other variations in rubber properties due to chlorination were detected. As a result of chlorination, the properties of the rubber are changed to create more electrically active groups that causes charges to better dissipate.
In relation to the invention, any chemical reaction, changing the structure of rubber, creating more active molecules of oxygen or other hydrophilic substances, in specific chlorination, grants rubber to have a better static discharge, ESD properties. In a summarized relation to the invention, a filler of a precipitate calcium carbonate, combined with a pigment of an organic nonmetal conjugated double bond derivative, specifically an orange Azo pigment having CAS No. 3520-72-7 or a Carbon Black pigment, each of them along with chlorination, will grant such rubber elastomers a better electrostatic discharge (ESD) properties.
Static electricity is a concern when working with sensitive electrical devices, for example semiconductor components. Any spark, small as it may be, might damage such parts. “Antistatic Gloves” or ESD gloves help to resolve such production issues. In addition, safety matters are of concern when dealing with possible explosions in oil and gas deliveries and facilities. Such danger exists where other explosive vapors are present. For example, in medicine production facilities, where alcohol is being used vastly, for sterilization. Sparks can cause an explosion of the alcohol vapors present in the atmosphere of the facility. “Antistatic Gloves” or ESD gloves resolves safety and productivity issues. They allow minor sparks to better travel through the glove to the operator and to the ground, dissipating the danger. In experimental evaluation of ESD properties of rubber films, antistatic properties are evaluated by a variety of testing. It can be evaluated by measuring the surface electrical resistance or resistivity, of the rubber film. The units are Ohm. It can be also evaluated by measuring the resistance of the volume of the rubber film, across the body of the film. The units are Ohms.
Previous studies have shown that a form-fitting glove with improved anti-static discharge and a method of manufacturing the glove with one layer or multi-layered utilizing a standard latex dip line (Piesker and Hansen, 2012); and that an antistatic rubber latex composition which includes carbon black as an antistatic agent and antistatic rubber gloves using the composition are provided (Kishihara and Ozawa, 2003). However, these two patents are directed to a different method of producing antistatic gloves and does not utilize chlorination. Another patent (Tsuwako et al., 2003) provides a handling glove capable of preventing the buildup of static charges and electric charge leakage and states the glove is coated with dissipative material such as nitrile rubber. However, this patent includes a different method of producing the glove, and does not utilize chlorination. Another patent (Kimura et al., 1992) provides a method of producing chlorinated rubber, However, it does not teach the use of the chlorinated rubber to make an antistatic rubber glove. Therefore, there is need to produce an antistatic rubber gloves with an improved electrostatic discharge (ESD) properties by adding various additives combined with chlorination in the process of preparation of rubber gloves.